1. Field of the Invention
The present invention concerns bidirectional transmission systems.
Half-duplex bidirectional transmission is a technique enabling bidirectional transmission on a single transmission medium in which each terminal station of the transmission system alternately sends and receives.
Depending on the speed at which the signals are transmitted over this medium, it may be necessary to allow for their transmission time and so it may be necessary to provide in the transmission format used periods allowing for these transmission times that cannot be used to transmit information. This is an obvious drawback in that it limits the amount of information that can be transmitted by means of such systems.
An object of the present invention is to avoid this drawback in the case of half-duplex bidirectional transmission systems which are also of the time division multiple access point-to-multipoint type.
The present invention is applicable to half-duplex bidirectional transmission systems of the point-to-multipoint type, i.e. enabling transmission between a central station and a plurality of remote stations, and more particularly to systems of this kind which comprise, between said central station and a concentration point, a transmission medium which is time-shared between the various remote stations, and, between said concentration point and each remote station, a respective transmission medium specific to each remote station and the lengths of which vary according to the location of the remote stations relative to the concentration point.
The present invention is even more specifically concerned with the situation in which said time-sharing of the transmission medium utilizes the TDMA (Time Division Multiple Access) technique with a transmission format structured in frames comprising different time slots assigned in a predetermined manner to respective different remote stations.
The present invention is applicable in particular to distribution networks used in the terminal part (close to the users) of a telecommunication network and particularly to distribution networks of this kind in which said transmission media are optical fibers and said concentration point is a passive optical coupler.